addpixsample [-radius <expr-rad>] [-systems <in-sys> <pix-sys>] <expr-lon> <expr-lat> <healpix-file>
Samples pixel data from an all-sky image file
in HEALPix format.
<healpix-file> argument must be
the filename of a table containing HEALPix pixel data.
The URL of such a file can be used instead, but local files
are likely to be more efficient.
give expressions for the longitude and latitude in degrees
for each row of the input table;
this is usually just the column names.
The long/lat must usually be in the same coordinate system
as that used for the HEALPix data, so if the one is in
galactic coordinates the other must be as well.
If this is not the case, use the
to give the input long/lat and healpix data coordinate system
The available coordinate system names are:
icrs: ICRS (Right Ascension, Declination)
fk5: FK5 J2000.0 (Right Ascension, Declination)
fk4: FK4 B1950.0 (Right Ascension, Declination)
galactic: IAU 1958 Galactic (Longitude, Latitude)
supergalactic: de Vaucouleurs Supergalactic (Longitude, Latitude)
ecliptic: Ecliptic (Longitude, Latitude)
<expr-rad>, if present,
is a constant or expression
giving the radius in degrees over which
pixels will be averaged to obtain the result values.
Note that this averaging is somewhat approximate;
pixels partly covered by the specified disc are weighted
the same as those fully covered.
If no radius is specified, the value of the pixel covering
the central position will be used.
<healpix-file> file is a table
with one row per HEALPix pixel and one or more columns
representing pixel data.
A new column will be added to the output table
corresponding to each of these pixel columns.
This type of data is available in FITS tables for a number of
all-sky data sets, particularly from the
see for instance the page on
(including dust emission, reddening etc)
WMAP 7 year data.
If the filename given does not appear to point to a file
of the appropriate format, an error will result.
Note the LAMBDA files mostly (all?) use galactic coordinates,
so coordinate conversion using the
may be appropriate, see above.
Syntax for the
<expr-rad> arguments is described in the manual.
This filter is somewhat experimental, and its usage may be changed or replaced in a future version.
Note: you may prefer to use the